1. Field of Invention
The present invention relates to a Doherty amplifier.
2. Background
In most communication systems, it is required that the power amplifier could operate with high efficiency and high linearity simultaneously. However, there is a tradeoff between the efficiency and the linearity with improvement in one of the two coming at the expense of the other of the two. Besides, many wireless communications systems, such as GSM (Global System Mobile Communication)/EDGE (Enhanced Data Rates for GSM Evolution), CDMA2000 (Code Division Multiple Access 2000), or WCDMA (Wideband Code Division Multiple Access)/LTE (Long Term in Evolution), or the like, require that the power amplifier could deliver a wide range of output power. As a result, being designed for the highest power level with maximum available efficiency, the power amplifiers in base stations tend to operate less efficiently at lower power levels consuming a lot of extra DC power. Therefore, it is a real challenge to design a power amplifier applicable to a base station that has high efficiency not only at maximum output power but also at lower power levels typically ranging from −6 dB and less, with minimum size and lower cost of implementation.